Engine speed control system

ABSTRACT

A method of controlling the engine speed of an internal combustion engine, the method providing the steps of determining the speed of the engine at a given time, determining the change in the speed of the engine from a previous determination of the engine speed, and using the values for engine speed and change in engine speed to determine whether a future event should be a combustion event or a non-combustion event.

BACKGROUND OF THE INVENTION

This invention relates to internal combustion engines, and in particulara method and control system for use in such engines to control therevolutionary speed thereof. The invention will in the main be describedin relation to a direct injection two-stroke spark ignition engine,although it is to be appreciated that use of the method and controlsystem in relation to other engine applications is also envisaged.

Internal combustion engines are used in a wide variety of applications,such as in motor vehicles (cars, all terrain vehicles and two-wheeledvehicles) and watercraft including personal watercraft (PWC's) andoutboard engines for boats. In many of these applications, it may beimportant in the operation of the engine to be able to control therotational speed of the engine.

For example, a requirement to limit engine speed may arise in order toprotect an engine from damage which could be sustained during overlyhigh speed operation, or to limit the overall speed of the vehicle beingpowered by the engine. Such speed limiting may be desirable in instanceswhere the operator of the vehicle is inexperienced or if maximum speedlimits are provided for a given situation.

PWC's are particularly susceptible to overspeed conditions as thesecraft are often operated at or near their maximum engine speed. Duringwave jumping for example, a popular activity of PWC enthusiasts, andduring rough water conditions, the driving mechanism of the PWC isliable to rise above the water level, thereby creating a sudden drop inload on the engine, and hence an associated increase in engine speed. Inthis regard and since it is common for PWC's to be operating at or closeto maximum engine speed when wave jumping or in rough water, it isimportant to avoid any “over-revving” of the PWC engine as this mayresult in damage to the engine.

In the past most engines simply had no maximum speed control except forthe engine's natural maximum limit, leaving the engine particularlysusceptible to damage from operation at overly high speed. Morerecently, mechanical devices such as governors have been used, anddevelopments in the electronic control of engines have resulted in agreater ability to control or restrict the maximum speed of internalcombustion engines.

For example, in one such development, it has been proposed to preventfurther increases in engine speed once the engine reaches a preset upperspeed limit by skipping combustion events. In one possible scenario, theignition event is simply not enabled, and the combustion event does notoccur. This method however has the disadvantage that fuel is stilldelivered into the combustion chamber, and passes out through the engineexhaust system into the environment, in an unburnt state. This is both asignificant waste of fuel and can be harmful to the environment.Additionally, residual unburnt fuel can remain in the combustion chamberand adversely affect a subsequent combustion event by reducing thepredictability and certainty with regard to the amount of fuel in thecombustion chamber.

Another known option is to reduce the fuelling level to the engine sothat reduced power is produced thereby and engine speed is reduced.However, whilst this appears to be a reasonable option, bulk air flowthrough the combustion chamber is not affected by simply reducing thefuelling levels, and the overall result, particularly in the case ofwide open throttle operation, may be enleanment of the air fuel ratio ofthe combustion mixture in the combustion chamber. Such enleanment canresult in lean misfire and the overheating of the engine, particularlyat high operating loads.

The present Applicant has developed a two-fluid fuel injection system asdisclosed in, for example, the Applicant's U.S. Pat. No. 4,693,224, thecontents of which are incorporated herein by reference. The method ofoperation of such a two-fluid fuel injection system typically involvesthe delivery of a metered quantity of fuel to each combustion chamber ofan engine by way of a compressed gas, generally air, which entrains thefuel and delivers it from a delivery injector nozzle. Typically, aseparate fuel metering injector, as shown for example in the ApplicantsU.S. Pat. No. 4,934,329, delivers, or begins to deliver, a meteredquantity of fuel into a holding chamber within, or associated with, thedelivery injector prior to the opening of the delivery injector toenable direct communication with a combustion chamber. When the deliveryinjector opens, the pressurised gas, or in a typical embodiment, air,flows through the holding chamber to entrain and deliver the fuelpreviously metered thereinto to the engine combustion chamber.

In an engine operated in accordance with such a two-fluid fuel injectionstrategy, there are therefore distinct events in the combustion process,including a fuel metering or fuel event, an air delivery or injectionevent (as opposed to the bulk air delivery into the combustion chamberwhich occurs separately), and an ignition event. The engine managementsystem typically required to implement such a strategy includes anelectronic control unit which is able to independently control each ofthe fuel, air, and ignition events to effectively control the operationof the engine on the basis of operator input. Accordingly, the use ofsuch a two-fluid fuel injection system allows combustion events to bepartially or completely cancelled, producing a non-combustion event in aselected cylinder.

In the context of this specification, unless otherwise indicated, an“event” is either a combustion event, or a non-combustion event whichoccurs where the combustion event would have occurred if it had beenscheduled.

Hence, in a two-fluid fuel injection system, it is possible for theelectronic control unit to simply cut one or more cylinders of theengine by simply providing no fuel for an event, the event then simplyconsisting of compressing air which is substantially free of fuel, andallowing it to expand again, thus not contributing to any additionalengine speed and avoiding the negative consequences of other forms ofengine speed control. However, simply cutting a fuel event may result ina certain degree of “drying” of the delivery injector nozzle which wouldstill have a quantity of air being delivered therethrough. This mayresult in the next combustion event upon reinstatement of the cutcylinder being less than satisfactory.

In a similar manner, it is possible for the electronic control unit tobypass or cut one or more cylinders of the engine by simply notinitiating an air event. Thus, any fuel which is metered into thedelivery injector nozzle is simply not delivered thereby, hence notcontributing to any additional engine speed. However, such a strategymay also have associated problems in that upon reinstatement of thepreviously bypassed cylinder, the next combustion event may result intwice as much fuel being delivered to a cylinder. That is, the previousundelivered fuel quantity together with a subsequent metered quantity offuel are delivered in the one injection event upon reinstatement of thepreviously bypassed cylinder.

It should be understood that cutting the ignition event as alluded tohereinbefore is still an option for producing a non-combustion event insuch a two-fluid injection system, but this option still possesses theassociated disadvantages as described hereinbefore.

Accordingly, in such a two-fluid injection system, it may be morebeneficial to ensure that neither the fuel event nor the air event occurwhen seeking to cut a cylinder and hence produce a non-combustion event.In this regard, in order to effectively produce a non-combustion eventin such a manner, it is obviously better to determine whether aparticular combustion event should be skipped, and then arrange thecancellation of the fuel and air events prior to the start of the actualfuel metering for the combustion event.

However, in the above-mentioned two-fluid fuel injection system, thestart of the fuel event, at high loads, may take place up to around 700degrees before top dead centre (BTDC) of the compression stroke of thecombustion event which is being scheduled, though it would more commonlyoccur at around 500-550 degrees BTDC for typical high load operation. Afurther complicating issue is that, together with the decision as towhether or not to provide a combustion event being made early, there maybe a number of events which will affect the engine speed which arealready scheduled to occur between the decision and the actual eventoccurring or not occurring. Further, the outcome of the impact of theevent on the engine speed may not be known until some time after topdead centre (ATDC), possibly at around 180 degrees ATDC. Hence, thedecision to have a combustion event or a non-combustion event iseffectively needing to be made some time before the outcome of anearlier scheduled event is known (i.e., upon the engine speed).

Such a delay may correspond to about five combustion or non-combustionevents in a typical two cylinder two-stroke engine and as a result ofthis, control of the engine speed can be unpredictable. That is, due tothe way in which fuel and air events are scheduled by the electroniccontrol unit, and also due to the processing delay within the electroniccontrol unit, a decision to allow or cancel a combustion event will needto be made effectively two to three events prior to when the scheduledevent would normally occur. This process is made somewhat more difficultby the fact that when this decision is made, depending on the engineoperating speed, a number of other combustion events or non-combustionevents may have already been scheduled and the effect that these eventswill have on the engine speed is unknown.

Whilst some of the above-mentioned difficulties are more pronounced intwo-fluid fuel injection systems, similar difficulties may also beexperienced with single fluid fuel injection systems.

BRIEF SUMMARY OF THE INVENTION

Accordingly, it is an object of the present invention to provide anengine speed control method which at least ameliorates some of the aboveproblems.

According to a first aspect of the present invention, there is provideda method of controlling the engine speed of an internal combustionengine, the method providing the steps of determining the speed of theengine at a given time, determining the change in the speed of theengine from a previous determination of the engine speed, and using thevalues for engine speed and change in engine speed to determine whethera future event should be a combustion event or a non-combustion event.

The determination of the change in the speed of the engine iseffectively used to provide an indication of the overall load that theengine is experiencing. Hence, this determination can take account of anumber of aspects which may effect the speed of the engine such as inparticular the load placed on the engine due to its working environment.For example, in the case of a marine application, the change in enginespeed and hence the overall load on the engine will be affected bywhether the driving mechanism of the engine is in or out of the water.

Conveniently, the method as described is used to control the enginespeed to a predetermined target speed. Hence, in determining whether afuture event should be a combustion event or a non-combustion event, themethod is providing for feed-forward control of the engine speed. Thatis, the method is applied to firstly effectively predict what the enginespeed will be after one or a number of fuelling events in the future ifthe operating conditions remain unchanged, and then to decide whetherthe next events should be combustion events or non-combustion events soas to target a predetermined engine speed setting.

Preferably, where it is determined that a noncombustion event isrequired, no fuel is supplied to the combustion chamber. Alternatively,ignition may be cut such that a noncombustion event results in therespective combustion chamber. Other means of generating anon-combustion event may also be implemented.

Conveniently, fuel is supplied to the engine via a two-fluid direct fuelinjection system, and where it is determined that a non-combustion eventis required, no fuel is metered into a delivery injector of thetwo-fluid fuel injection system and no air is passed through thedelivery injector into the combustion chamber. Hence, in such atwo-fluid injection system, both the air and fuel events are cancelledwhere it is determined that a non-combustion event is required.

Preferably, a decision as to whether a particular event is to be acombustion event or a non-combustion event is made prior to thebeginning of the fuelling operation for that event. The decision as towhether a particular event is to be a combustion event or anon-combustion event may be made at over 360 degrees BTDC for the eventwhich is being determined, and may be at around 710 degrees BTDC.Essentially, at higher engine speeds, a decision will need to be made atsuch an earlier time as it is possible that one or more events arealready scheduled to occur prior to the event for which the decision isbeing made. This is particularly the case for two-fluid fuel injectionsystems where it is typical at higher engine speeds for a number of fueland air events to be already scheduled to occur prior to the event uponwhich the decision to cancel or enable the event is being made.

Preferably, the method is applied during high speed operation of theengine, and is used to avoid the occurrence of overspeed conditions.Conveniently, the method is applied to control the engine speed duringhigh speed operation to a threshold target engine speed. Hence, themethod is used to provide an indication of what the engine speed will beafter one or a number of events in the future and to then control theengine speed to the threshold target speed by enabling a subsequentcombustion event to occur or by deciding that a non-combustion eventshould occur. Thus, the method enables the operator or rider of thecraft within which the engine is arranged to maintain the engine speedat or close to the maximum allowed speed without damaging the engine.

Accordingly, the method provides for feed-forward overspeed control bytargeting a predetermined threshold engine speed and scheduling asequence of combustion events and/or non-combustion events which willmaintain the engine speed as close to the target engine speed aspossible.

Preferably, the method is applied when the engine speed exceeds apredetermined entry speed. Conveniently, this entry speed is set at avalue lower than the target or threshold speeds to which the enginespeed is controlled. Hence, as the speed of the engine climbs towardsthe predetermined target or threshold speed, it will preferably only becontrolled according to the present method once it exceeds the lowerentry engine speed. This entry engine speed may typically be 1000 rpmless than the target engine speed.

Preferably, an adaption value is calculated on the basis of engine speedand the effective load levels as determined for a given event. Theadaption value may be used in determining whether the future eventshould be a combustion event or a non-combustion event. Where theeffective load on the engine is high, the adaption value may be set soas to increase the likelihood of a combustion event as compared to anon-combustion event. This is typically consistent with small changes inthe engine speed such as for a marine engine operating at high speedwith the driving mechanism of the engine continuously being located inthe water. Where the effective load on the engine is low, the adaptionvalue may be set so as to increase the likelihood of a non-combustionevent as compared to a combustion event. This is typically consistentwith larger changes in the engine speed such as when the drivingmechanism of a marine engine operating at high speed leaves the water.

Preferably, a filter is applied to the rate of change of the adaptionvalue to limit the rate of change of the adaption value. The filter maybe dependent on whether the load on the engine is increasing ordecreasing.

Conveniently, the fuelling level supplied to the engine may be used as adetermination of the load on the engine. Conveniently, once it has beendetermined that the engine speed is likely to exceed the predeterminedthreshold engine speed, a preset pattern of combustion events andnon-combustion events is implemented in at least one injector to controlthe engine speed in relation to the threshold engine speed.

According to a second aspect of the present invention, there is provideda control system for an internal combustion engine in which currentengine speed and the change in engine speed from a previousdetermination are taken into account when determining whether a futureevent should be a combustion event or a non-combustion event.

Preferably, the second aspect of the present invention provides acontrol system for operation in accordance with each of the preferredembodiments of the first aspect of the present invention.

Specifically, there may be provided a system for targeting apredetermined threshold or target engine speed and scheduling a sequenceof combustion events and/or non-combustion events which will maintainthe engine speed as close to the target engine speed as possible.

The system may also be further adapted to provide for limitation ofoverspeed conditions in the use of the internal combustion engine.

Preferably, the system may provide an adaption value, which iscalculated on the basis of engine speed and the effective load levels asdetermined for a given event. The adaption value may be used indetermining whether a future event should be a combustion event or anon-combustion event.

According to a third aspect of the present invention, there is providedan Electronic Control Unit arranged to implement a control strategy foran internal combustion engine, in which current engine speed and thechange in engine speed from a previous determination are taken intoaccount when determining whether a future event should be a combustionevent or an non-combustion event.

According to a fourth aspect of the present invention, there is provideda method of controlling the rotational speed of an internal combustionengine, the method including the steps of determining whether the enginespeed is likely to exceed a predetermined threshold engine speed, andimplementing a pattern of combustion events and non-combustion events inat least one engine cylinder in order to modify the effective fuelinglevel to the engine cylinders so as to control the engine speed inrelation to the threshold engine speed.

Preferably, the prevailing fueling level for an individual cylinder inwhich a combustion event is to occur is not altered. That is, whilst theeffective fueling level to the engine may, for example, be reduced, thefueling level to the individual cylinders which are not cut (i.e.,within which a combustion event will be allowed to occur) will remainunchanged. In this way, the operational cylinders will continue tooperate with the same prevailing air/fuel ratio.

Preferably, the method of controlling the speed of the engine isaffected so as to limit the engine speed. Preferably, the determinationof whether the engine speed is likely to exceed the predeterminedthreshold engine speed is based on the engine speed determined for agiven time. Preferably, the requirement for reduced speed may bedetermined on the basis of both the engine speed and the effective loadon the engine whereby the latter is established by determining thechange in engine speed from a previous determination thereof. In thisregard, once it is determined that the engine speed will exceed apredetermined threshold engine speed and the effective load on theengine has been determined, the effective fueling level required tomaintain the engine speed at the threshold engine speed can becalculated. On the basis of this desired effective fueling level, one ofa number of preset patterns of combustion events and non-combustionevents can be implemented to control the engine speed.

Preferably, the method of controlling the speed of the engine iseffected by implementing a repeatable pattern of combustion eventsand/or non-combustion events.

Preferably, the method is used to avoid overspeed conditions in theengine operation. The pattern of combustion events and non-combustionevents may provide a greater number of non-combustion events persequence when there are effectively lower load conditions on the engine,and a lower number of non-combustion events per sequence when the engineeffectively experiences higher load conditions.

Accordingly, the method of prescribing a sequence of combustion eventsand/or non-combustion events results in a reduction of the torque outputof the engine and hence the speed thereof in a predictable manner. Thisis achieved without regulating or reducing the fuelling of a number ofevents and hence without running a variety of air/fuel ratios betweendifferent engine cylinders. This is particularly applicable to wide openthrottle operation where the engine speed is typically close to themaximum operating speed of the engine wherein reduced fuelling levelsmay cause engine detonation and overheating.

Unless clearly indicated otherwise, the expression “top dead centre”(TDC) shall be taken to refer to the location at top dead centre of apiston within a cylinder of a corresponding engine during the eventwhich is being determined by the method or control system of the presentinvention. A reference to an angle “before top dead centre” (BTDC) or“after top dead centre” (ATDC) shall be taken as a reference to thenumber of degrees of rotation of the engine before or after the top deadcentre position for the event which is being determined by the method orcontrol system of the present invention.

The method and control system of the current invention is particularlyapplicable to marine and PWC applications. It is also however conceivedthat this invention may also be applicable to other engine applicationsand hence the invention is not deemed to be limited in its application.

Further, whilst the current invention is particularly applicable to dualfluid fuel injection systems, it is not intended to be limited as suchand can be equally applicable for use with single fluid fuel injectionsystems. Still further, the current invention has applicability to bothtwo and four stroke cycle engines.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described in relation to a preferredembodiment of the invention, and with particular reference to theaccompanying drawings, in which:

FIG. 1 is a schematic representation of fuel and air event timing in atwo-fluid direct fuel injection system in a two cylinder engine;

FIG. 2 is an illustrative mapping of engine speed over time for highspeed operation where there exists a low effective load on the engine;and

FIG. 3 is an illustrative mapping of engine speed over time for highspeed operation where there exists a high effective load on the engine.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Turning firstly to FIG. 1, this illustration sets out the fuel meteringevent timings and delivery injector air flow timings with respect tocrank angle for a series of combustion events in a two cylinder,two-stroke, two-fluid direct injection engine. Zero degrees crank anglehas been set for the purposes of this example as the TDC for the eventfor which a decision is being made with regard to whether a combustionevent or a non-combustion event is to take place. In this example, theevent in question is event VII as indicated in FIG. 1 and the TDC forthis event is indicated by the reference Y.

In this illustration, Row A shows the crank angle timings of thefuelling or fuel metering event for the first cylinder of the engine,whilst Row B shows the timings of the delivery injector air event forthe first cylinder. Row C shows the fuelling event timings for thesecond cylinder of the engine, whilst Row D shows the delivery injectorair event timings for the second cylinder of the engine. The injectorair and fuel events for the first and second cylinders respectively areapproximately 180 degrees out of phase, as is usual in such two cylinderengines.

The ignition event generally occurs at around TDC for the respectivecylinder following the completion of the injector air flow event, andthe fuel event, the air event and the ignition event together make upthe combustion event. For a non-combustion event, any or all of thesethree events may be scheduled not to occur, though it is preferred thatnone of the events occur for most efficient operation of the engine. Asnoted above, this example focuses specifically on the decision as towhether or not event VII should be a combustion event or anon-combustion event.

The first event shown is indicated by reference numeral I, which istaken to have occurred at approximately 1080 degrees BTDC. The physicaloutcome of this event in terms of its effect on the engine speed areknown for the purposes of the decision to be made for event VII. Enginespeed is typically detected by known electronic means, and the effect onengine speed as a result of a particular event which has actuallyoccurred is obtainable approximately 180 degrees after top dead centreof that event. Hence, the effect on engine speed of event II, which istaken to have occurred at around 900 degrees BTDC, will be known atapproximately 720 degrees BTDC. As the decision regarding whether eventVII should be a combustion event or a non-combustion event is not madeuntil approximately 710 degrees BTDC, indicated on FIG. 1 by thereference X, the actual physical outcome of event II can be taken intoaccount when making a decision regarding event VII.

The actual outcomes in terms of the effect on engine speed of the nextfour events, III, IV, V, and VI, are not available, as these have notyet been determined at the time of needing to make the decisionregarding event VlI. In fact, events IV, V and VI have not yet occurred.However, the electronic controller does take into account whether eachof these events is a combustion event or a non-combustion event, asthese decisions have been made and are known.

The electronic controller has also calculated an adaption value based onthe effective load on the engine. As alluded to hereinbefore, theadaption value is calculated to take account of the effect a combustionevent or a non-combustion event will have on the speed of the engine.For example when the engine is experiencing a high effective load, acombustion event may cause a small increase in the engine speed whereasa non-combustion event may cause a large decrease in the engine speed.Similarly, when the engine is experiencing a low effective load, acombustion event may cause a large increase in engine speed whilst anon-combustion event may cause a small decrease in engine speed. Byunderstanding the effect a combustion event or a non-combustion eventmay have on the speed of the engine and assigning an adaption valuebased on this effect, such a value can then be applied to affect thedesired control of the engine speed. The utilisation of such an adaptionvalue enables the engine speed to be targeted more closely to themaximum engine speed limit. As alluded to hereinbefore, a measure of theeffective load on the engine may be determined from a comparison of thea prevailing engine speed and a previous determination of engine speed.

On the basis of the known engine speed (detected at approximately 720degrees BTDC), the adaption value, and the known decisions on eventsIII, IV, V and VI, the controller predicts what the engine speed will beat point Y. Having preset speed limits and/or a target maximum speed,the controller then determines whether event VII should be a combustionevent or a non-combustion event. This occurs so that the controller caneffect feed-forward control of the engine speed to a target enginespeed.

If the decision is that a combustion event is required, a full fuellingevent is scheduled. For high load, high speed operation, the fuellingevent VlI will start shortly after that decision. Generally, a level ofinherent delay in the system will form part of the delay from thedecision to start the fuelling event and the actual start of fuel flow.If however the decision is that the event should be a non-combustionevent, the fuel event is not commenced, and the air event is notscheduled, and does not occur.

The actual outcome of event VII in terms of its affect on the speed ofthe engine will not be known until approximately 180 degrees ATDC, asindicated at point Z in FIG. 1. Once the actual outcome and thepredicted outcome are known, they can be compared and the adaption valuealtered if necessary to reflect any changed conditions under which theengine is operating.

It should be understood that a system such as that described above canbe used to provide feed-forward overspeed control to bring the speed ofan engine to within a target value. This occurs by predicting what theengine speed will be after one or a number of future fuelling eventsshould engine operating conditions remain unchanged. Based on thisprediction, the combustion events can be enabled or cancelled in orderto achieve a predetermined target engine speed. Such an overspeedcontrol system would typically be implemented such that the system onlybecomes operational once a predetermined entry speed has been surpassed,that is, once the engine speed gets within a certain range of the targetspeed.

To better understand the process of determining whether a combustionevent will occur or not, consideration is now given to FIGS. 2 and 3.Both of these figures show illustrative examples of how engine speedmight be affected over time when the present invention is applied toengine operation.

FIG. 2 in particular illustrates a scenario where the engine isoperating under relatively low load conditions. Under such conditions,it can generally be said that a combustion event will have a greaterimpact on the current speed, increasing it significantly, whilst anon-combustion event will have a lesser impact on the current speed,reducing it by a smaller amount. This is because the lower load allows agreater degree of “freewheeling” by the engine on non-combustion events,and because a lower resistance is provided to acceleration as a resultof a combustion event due to the lower loading of the engine. Forexample, in regard to a PWC or marine engine, such a low load conditionwould equate to when the driving mechanism is out of the water.

FIG. 3 on the other hand illustrates a scenario where the engine isoperating under relatively high load conditions. Under such conditions,a combustion event will have a lesser impact on the current speed,increasing it by a relatively small amount, whilst a non-combustionevent will have a relatively greater impact on the current speed,decreasing it significantly. Once again, this is because the higher loadprovides a greater drag on the engine, making it tend to slow down,whilst providing a strong resistance to increases in speed. Again,taking the PWC or marine engine example, such a high load conditionwould equate to when the driving mechanism of the engine is pushing thecraft through the water.

In relation to FIG. 2 in particular, it can be seen that in the initialperiod shown in the graph, the engine speed is increasing steadilytowards the target maximum. Each point on the graph represents acombustion event, and the solid line indicates the actual speed of theengine, with the dotted lines representing the engine controller'sprediction of the speed which would have been attained if the oppositedecision had been made as to whether a combustion or non-combustionevent was to take place. The engine speed is assumed to have exceeded athreshold entry speed such that the method of the present invention isnow being used to predict the future engine speed.

At around the time of the event 20, the decision as to whether event 24should be a combustion event or not is made. The controller determinesthat a combustion event will result in an outcome speed as indicated atevent 25 and that a non-combustion event will result in an outcome speedas indicated at event 25′. As both of the alternative speeds are belowthe target maximum speed, the controller selects the higher of these twospeeds as being acceptable, and schedules a combustion event. As suchthe engine speed continues to rise to event 25.

At around the time of the event 21, the decision as to whether event 25should be a combustion event or not is made. The controller determinesthat a combustion event will result in an outcome speed as indicated atevent 26′ and that a non-combustion event will result in an outcomespeed as indicated at event 26. As the speed indicated by event 26 isnearer to the target speed than the speed indicated at event 26′, anon-combustion event is selected and as a result the speed will drop tothat indicated at event 26. This procedure is continued, with the targetmaximum speed being sought by the engine controller until the engineoperator allows the RPM to fall below the target range, and normaloperation is resumed. That is, once the engine speed falls below thethreshold entry speed, the method of the present invention is not usedand normal operation resumes.

A similar procedure is followed in relation to the high load scenarioillustrated in FIG. 3. The engine speed initially increases at a slowerrate to the low load scenario, due to the higher load on the drivingmechanism of the engine. The decision as to whether event 35 should be acombustion event or not is made at around the time of event 31. Thecontroller determines that a combustion event will result in an outcomespeed as indicated at event 36 and that a non-combustion event willresult in an outcome speed as indicated at event 36′. As the speedindicated by event 36 is nearer to the target speed than the speedindicated at event 36′, a combustion event is scheduled and as a resultthe speed will rise to that indicated at event 36. Once again thisprocedure continues with event 37 being scheduled as a non-combustionevent, causing a drop in RPM to the level indicated at event 38.

In FIG. 3, the adaption parameter is set to indicate high loadoperation. As such, the estimate of the future speed on which thedecision to provide a combustion event or a non-combustion event isbased will be lower than if the adaption parameter was set for low load.This is clearly indicated in FIG. 3 in that the predicted fall in RPMresulting from a non-combustion event is substantially greater than thepredicted fall in the case of a non-combustion event illustrated in FIG.2 in which the adaption parameter is set to indicate low load operation.Similarly, the predicted rise in RPM resulting from a combustion eventin the case of FIG. 3 is substantially lower than the predicted riseresulting from a combustion event illustrated in FIG. 2.

Under steady state conditions, a repetitive pattern of combustion andnon-combustion events may be established to maintain the target maximumspeed. This pattern will be dependent on the adaption value allocated tothe system at the time, and can be altered in accordance with thechanging of the adaption value. Naturally, if operating conditionschange, and cause a change in the engine speed, the pattern ofcombustion and non-combustion events can be altered to limit the enginespeed to it's correct level. Further, the application of a repetitivepattern of combustion and non-combustion events to control engine speedwould normally only occur once the engine speed had exceeded thepredetermined threshold entry speed and hence was within a certain rangeof the target maximum speed.

Generally, the higher the loading on the engine during speed limitationby this method, the lower the number of non-combustion events percombustion event. Similarly, the lower the loading on the engine, thegreater the number of non-combustion events per combustion event. Forexample, high speed/high load operation may involve a pattern of twocombustion events for each noncombustion event, whilst high speed/lowload operation may involve a pattern of three non-combustion events foreach combustion event.

It needs to be understood that in circumstances where a repetitivepattern or sequence of combustion and non-combustion events isestablished to control the engine speed, each combustion event uses anormal, mapped fuelling amount. This method of control of the enginespeed reduces the average fuelling level supplied to the engine over anumber of events without altering the normal, mapped fuelling levels.Therefore, there is no need for the engine to operate under a variety ofair/fuel ratios when the engine is operating at or close to a presetmaximum speed, thereby reducing the possible risks of detonation andengine overheating.

By selecting a preset sequence of combustion and non-combustion events,the effective fuelling of the engine can be controlled as is shownbelow. The following example shows typical results achievable in atwo-cylinder engine.

SEQUENCE EFFECTIVE FUELLING 1 non-combustion event every 3 events 0.83 ×normal fuelling level for one cylinder (ie: 5 of 6 engine events aremaintained) 1 non-combustion event every 2 events 0.75 × normal fuellinglevel for one cylinder (ie: 3 of 4 engine speed events are maintained) 1non-combustion event every 3 events 0.66 × normal fuelling level forboth cylinders (ie: 4 of 6 engine events are maintained) 1non-combustion event every 2 events 0.5 × normal fuelling level for bothcylinders (ie: 2 of 4 engine events are maintained) 2 non-combustionevents every 3 events 0.33 × normal fuelling level for both cylinders(ie: 2 of 6 engine events are maintained) 3 non-combustion events every4 events 0.25 × normal fuelling level for both cylinders (ie: 2 of 8engine events are maintained) 4 non-combustion events every 5 events 0.2× normal fuelling level for both cylinders (ie: 2 of 10 engine eventsare maintained)

By controlling the engine speed using such a method, the user is able toexperience a smooth, repeatable engine tone. This is desirable in marineapplications, particularly PWC applications, as such craft oftenexperience considerable time both in and out of the water at highspeeds. Furthermore, a simple form of the strategy wherein differentpreset sequences are implemented based on the corresponding achievementof different predetermined threshold engine speed levels may beparticularly applicable to certain outboard marine engines which may attimes operate close to an upper threshold speed limit but in areasonably steady or stable operating environment.

Whilst much emphasis has been placed upon utilising the described systemand method to control engine over-speed conditions, the system andmethods described are equally applicable to other scenarios where enginespeed needs to be limited and/or controlled. Such applications couldextend to use as a “child mode” or “novice mode” of operation, wherebythe engine speed of various vehicles/crafts is limited to allow safeoperation by children and the like. The described system and methodcould also be employed as a “limp-home” mode for various engines wherebythe need to maintain the engine speed below a low threshold speed isrequired to avoid further engine damage or failure.

Hence, the method and system as described above may provide substantialbenefits for the operation and maintenance of an engine to which it isapplied. The potential for damage to the engine is greatly reduced bythe avoidance of over-revving of the engine in situations where suchover-revving has been known to occur in the past. Such situationsinclude applications where load may be suddenly removed from the engine.A good example of this is in the use of a personal water craft, wherethe craft may become airborne, causing a sudden loss in loading on theengine, and a resultant surge in engine speed.

The present method and system is particularly (though not exclusively)applicable for use in dual fluid fuel and air injection systems wherefuel metering is performed independently of fuel delivery to the enginecombustion chambers. Such a system is particularly conducive to theapplication of the present invention which enables both the fuel and airevent for a combustion event to be cut providing for a more satisfactoryreinstatement of engine operation.

Although the present invention has been described in relation toparticular embodiments and applications, it is envisaged that theinvention will have broad applicability to a range of apparatus in therelevant field. The embodiments of the present invention have beenadvanced by way of example only, and modifications and variationstherefrom are possible without departing from the scope of the appendedclaims.

What is claimed is:
 1. A method of controlling the engine speed of aninternal combustion engine, the method providing the steps ofdetermining the speed of the engine at a given time, determining thechange in the speed of the engine from a previous determination of theengine speed, and using the values for engine speed and change in enginespeed to determine whether a future event should be a combustion eventor a non-combustion event wherein the engine has a direct injectionsystem and a fuel event is not scheduled when it is determined that anon-combustion event is required.
 2. A method according to claim 1,wherein the determination of the change in the speed of the engine fromthe previous determination of engine speed provides an indication of theeffective load on the engine.
 3. A method according to claim 2, whereinthe determination of the effective load on the engine is applied toprovide for feed forward control of the engine speed.
 4. A methodaccording to claim 1, including firstly predicting what the engine speedwill be after at least one fuelling event in the future if the operatingconditions remain unchanged, and then deciding whether the next event tobe scheduled should be a combustion event or a non-combustion event soas to target a predetermined engine speed setting.
 5. A method accordingto claim 1, including supplying no fuel to an engine cylinder when it isdetermined that a said non-combustion event is required.
 6. A methodaccording to claim 5, including preventing ignition within an enginecylinder when it is determined that a said non-combustion event isrequired.
 7. A method according to claim 1, wherein the engine has atwo-fluid direct fuel injection system.
 8. A method according to claim7, wherein a decision as to whether a particular event is to be acombustion event or a non-combustion event is made prior to the fuelmetering event for that event.
 9. A method according to claim 1,including determining whether a future event is to be a combustion eventor a non-combustion event at over 360 degrees BTDC relative to theoccurrence of said future event.
 10. A method according to claim 9,including determining the future event at about 710 degrees BTDCrelative to the occurrence of said future event.
 11. A method accordingto claim 1, including applying said method during high speed operationof the engine to thereby avoid the occurrence of overspeed conditions.12. A method according to any one of claims 1, 2, and 6, includingcontrolling the engine speed to a threshold target engine speed.
 13. Amethod according to claim 12, including applying the method once theengine speed exceeds a predetermined entry speed.
 14. A method accordingto claim 13, including setting the entry speed at a value lower than thethreshold target speed to which the engine speed is controlled.
 15. Amethod according to any one of claims 1, 2, and 6, including calculatingan adaption value on the basis of engine speed and effective load levelsas determined for the future event, the adaption value being used indetermining whether the future event should be a said combustion eventor a said non-combustion event.
 16. A method according to claim 15,wherein when the effective load is high, the adaption value is set so asto increase the likelihood of a said combustion event as compared to asaid non-combustion event, and wherein when the effective load is low,the adaption value is set so as to increase the likelihood of a saidnon-combustion event as compared to a said combustion event.
 17. Amethod according to claim 15, wherein a filter is applied to the rate ofchange of the adaption value to limit the rate of change of the adaptionvalue.
 18. A method according to claim 17, wherein the filter isdependent on whether the load on the engine is increasing or decreasing.19. A method according to claim 18, wherein the fuelling level suppliedto the engine is used as an indication of the load on the engine.
 20. Amethod according to any one of claims 1, 2, and 6, wherein a presetpattern of combustion events and non-combustion events is implemented inat least one engine cylinder to control the engine speed.
 21. A methodaccording to any one of claims 1, 2, and 6, wherein the method isemployed as a limp-home mode whereby the need to maintain the enginespeed below a low threshold speed is required to avoid engine damage orfailure.
 22. A control system for controlling an internal combustionengine utilizing a method according to claim
 1. 23. An engine controlunit (ECU) implemented to control an internal combustion engine inaccordance with a method according to claim
 1. 24. A control system foran internal combustion engine in which current engine speed and thechange in engine speed from a previous determination are taken intoaccount when determining whether a future event should be a combustionevent or a non-combustion event.
 25. A control system according to claim24, wherein the system targets a predetermined threshold engine speedand schedules a sequence of at least one of combustion events andnon-combustion events for maintaining the engine speed as close to thetarget engine speed as possible.
 26. A control system according to claim24, wherein the system is further adapted to provide for limitation ofoverspeed conditions in the use of the internal combustion engine.
 27. Acontrol system according to claim 24, wherein the system provides anadaption value, which is calculated on the basis of engine speed and theeffective load levels as determined for the future event, the adaptionvalue being used in determining whether the future event should be acombustion event or a non-combustion event.
 28. A method of controllingthe rotational speed of an internal combustion engine, the methodincluding the steps of determining whether the engine speed is likely toexceed a predetermined threshold engine speed, and implementing apattern of combustion events and non-combustion events in at least oneengine cylinder in order to modify the effective fueling level to theengine cylinders so as to control the engine speed in relation to thethreshold engine speed.
 29. A method according to claim 28, wherein theprevailing fuelling level for an individual cylinder in which acombustion event is to occur is not altered.
 30. A method according toclaim 23, wherein the method of controlling the speed of the engine isaffected so as to limit the engine speed.
 31. A method according toclaim 28, wherein the requirement for reduced speed is determined on thebasis of both the engine speed and the effective load on the enginewhereby the latter is established by determining the change in speedfrom a previous determination thereof.
 32. A method according to claim31, wherein the effective load on the engine required to maintain theengine speed at the threshold engine speed, or said effective fuellinglevel is used to select one of a number of preset patterns of combustionevents and non-combustion events.
 33. A method according to claim 28,wherein the method is used to avoid overspeed conditions in the engineoperation.
 34. A method according to claim 28, wherein the pattern ofcombustion events and non-combustion events provide a greater number ofnon-combustion events per sequence when there are effectively lower loadconditions on the engine, and a lower number of non-combustion eventsper sequence when the engine effectively experiences higher loadconditions.
 35. The method as recited in claim 1, wherein the engine hasa single fluid direction injection system.